Drawing machines are known for metal products, such as solid or tubular bars, which comprise a drawing assembly provided with two counter-rotating tracks, opposite each other with respect to a drawing axis.
Each track includes a plurality of links, constrained to each other in sequence, on each of which a drawing clamp is mounted which, during use, presses against at least one bar subjected to drawing.
In particular, each drawing clamp of one track cooperates with a corresponding drawing clamp present on the opposite track in order to clamp the bar subjected to drawing from opposite sides, in a segment that has already been drawn.
Each clamp is provided with a recess, which is shaped specifically and coordinated with respect to the cross section of the bar in the segment that has already been drawn.
In this way, the bar to be drawn is clamped between two recesses of two opposite clamps, and the rotation of the two tracks performs the clamping and substantially continuous drawing of the bar, to carry out the drawing process.
The drawing clamps are removable from the respective links, so they can be completely removed in the event of wear or if the section of the bar to be drawn is varied.
It is known to produce a high number of different series of replaceable drawing clamps, normally 4-5 series for solid bars and 10 or more series for tubular products.
Each series of drawing clamps has the corresponding recess with sizes that differ from one series to the other, so that each series of drawing clamps is suitable to clamp efficiently a coordinated range of bars with different diameters.
Each drawing clamp can be selectively clamped inside a housing seating made in the corresponding link by corresponding rapid attachment/detachment means associated to the link, an example of which is shown in WO 01/14076 A1.
A solution is also known, from WO-A-2009/037320 (WO'320) in the name of the present Applicant, in which each drawing clamp comprises two or more recesses with different sizes from each other, and in each of which a determinate range of cross sections of the metal products to be subjected to drawing is able to be positioned. In this way it is obtained that the same clamp, with at least two recesses of different sizes, positioned for example adjacent to each other in a transverse direction with respect to the drawing axis, is able to guarantee the efficient clamping of at least two different ranges in size of metal product subjected to drawing. To pass from one range in size to another, it is sufficient to translate the clamps, or more generally move them, with respect to the link, in order to align the desired recess with the drawing axis and with the product subjected to drawing.
Drawing assemblies are known in which each link comprises a rapid attachment/detachment device, provided with a central clamping element and a corresponding activation element, to clamp the corresponding clamp inside the housing seating stably and removably.
For example, in the rapid attachment/detachment device described in the above application WO'320, the clamping element is a ball, while the activation element is defined by a thruster comprising in its upper part a cavity with a substantially semi-spherical shape, which functions as a cam profile for positioning the ball.
The solution described in this document, although efficient and precise in allowing a rapid change of the drawing clamps, and also able to considerably reduce the times and costs of replacement and maintenance of the drawing clamps, may be subject as time passes to bevels and plays occurring between the ball and the link. Furthermore, the ball may not guarantee a totally secure and precise positioning of the drawing clamp because of the fact that its portion that protrudes from the link, and causes the interference needed to maintain the position of the drawing clamp, is reduced (generally in the order of 2-3 mm). Moreover, with use, there is also the risk that the ball may deform and become oval. This can negatively affect the correct positioning along the drawing axis of the recess being used.
It is also known that it is necessary to carry out the detachment of the drawing clamps from the respective link of the track rapidly and safely.
One purpose of the present invention is to provide a drawing assembly for drawing machines that allows to clamp efficiently bars with different cross sections and/or sizes, and which has drawing clamps able to guarantee attachments and detachments that are safe under all conditions of use, retaining efficiency even as time passes and after long periods of use.
Another purpose of the present invention is to obtain a drawing assembly in which replacing the drawing clamps is rapid and easy, with lower costs and times of both production and management than the state of the art.
Another purpose of the present invention is to provide a drawing assembly for drawing machines that is compact and in which it is possible to replace or move the drawing clamps independently of the position of the links along each of the tracks, in order to clamp bars with cross sections of different shapes and/or sizes efficiently.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.